First Gas-Phase Detection of Dimethylstannylene and Time-Resolved Study of Some of Its Reactions

Abstract

Using a laser flash photolysis/laser probe technique, we report the observation of strong absorption signals in the wavelength region 450-520 nm (highest intensity at 514.5 nm) from four potential precursors of dimethylstannylene, SnMe(2), subjected to 193 nm UV pulses. From GC analyses of the gaseous products, combined with quantum chemical excited state CIS and TD calculations, we can attribute these absorptions largely to SnMe(2), with SnMe(4) as the cleanest source of the species. Kinetic studies have been carried out by time-resolved monitoring of SnMe(2). Rate constants have been measured for its reactions with 1,3-C(4)H(6), MeC[triple bond]CMe, MeOH, 1-C(4)H(9)Br, HCl, and SO(2). No evidence could be found for reaction of SnMe(2) with C(2)H(4), C(3)H(8), Me(3)SiH, GeH(4), Me(2)GeH(2), or N(2)O. Limits of less than 10(-13) cm(3) molecule(-1) s(-1) were set for the rate constants for these latter reactions. These measurements showed that SnMe(2) does not insert readily into C-H, Si-H, Ge-H, C-C, Si-C, or Ge-C bonds. It is also unreactive with alkenes although not with dienes or alkynes. It is selectively reactive with lone pair donor molecules. The possible mechanisms of these reactions are discussed. These results represent the first visible absorption spectrum and rate constants for any organo-stannylene in the gas phase.

Theoretical Study on the Reactivities of Stannylene and Plumbylene and the Origin of their Activation Barriers

“…This computational result is consistent with the experimental observation that Me 2 Sn is unreactive towards C À H bonds. [8] Likewise, my theoretical findings also suggest that Me 2 Ge does not insert readily into the CÀH bond, which has been confirmed by experimental works. [20] Silane insertion reactions: The geometrical results from the theoretical study on silane insertion reactions [Eq.…”

“…The principal motivation for this research was a remarkable recent experimental discovery by Walsh et al [8] who, using a laser flash photolysis/laser probe technique, showed that Me 2 Sn does not insert readily into CÀH, SiÀH, GeÀH, CÀC, SiÀC, or GeÀC bonds. It is also unreactive towards alkenes, although not towards dienes or alkynes.…”

“…My aim is therefore to search for a general theory of reactivity for carbene and its heavier analogues and to delineate the significant role played by their singlet-triplet energy separations (vide infra). To mimic the experimental observations of Walsh et al, [8] I calculated the potential energy surfaces of five insertion reactions [Eqs. (1)- (5)] and two addition reactions [Eqs.…”

“…These theoretical findings have been confirmed by experimental observations. [8,20,21] Germane insertion reactions: The stationary points shown in 5 were located for each germane insertion reaction [Eq. (3)] at both the DFT and CCSD(T) levels of theory.…”

“…These theoretical investigations are in agreement with some available experimental findings, especially for the germylene [20,22] and stannylene cases. [8] Methanol insertion reactions: The reaction of Me 2 X with ntype lone pair donors such as MeOH was also studied in this work. Selected geometrical parameters of reactants (Me 2 X + MeOH), precursor complex, TS, and insertion product for Equation (4) are collected in Figure 5.…”